linux-kernel - Re: [RFC PATCH v4 03/12] PM: Introduce an Energy Model management framework

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Date:   Thu, 5 Jul 2018 16:32:49 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rjw@...ysocki.net, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        mingo@...hat.com, dietmar.eggemann@....com,
        morten.rasmussen@....com, chris.redpath@....com,
        patrick.bellasi@....com, valentin.schneider@....com,
        vincent.guittot@...aro.org, thara.gopinath@...aro.org,
        viresh.kumar@...aro.org, tkjos@...gle.com, joel@...lfernandes.org,
        smuckle@...gle.com, adharmap@...cinc.com, skannan@...cinc.com,
        pkondeti@...eaurora.org, juri.lelli@...hat.com,
        edubezval@...il.com, srinivas.pandruvada@...ux.intel.com,
        currojerez@...eup.net, javi.merino@...nel.org
Subject: Re: [RFC PATCH v4 03/12] PM: Introduce an Energy Model management
 framework

On Thursday 05 Jul 2018 at 17:06:29 (+0200), Peter Zijlstra wrote:
> On Thu, Jun 28, 2018 at 12:40:34PM +0100, Quentin Perret wrote:
> > +/* fd_update_cs_table() - Computes the capacity values of a cs_table
> > + *
> > + * This assumes a linear relation between capacity and frequency. As such,
> > + * the capacity of a CPU at the n^th capacity state is computed as:
> > + *           capactity(n) = max_capacity * freq(n) / freq_max
> > + */
> 
> Broken comment style
> 
> > +static void fd_update_cs_table(struct em_cs_table *cs_table, int cpu)
> > +{
> > +	unsigned long cmax = arch_scale_cpu_capacity(NULL, cpu);
> > +	int max_cap_state = cs_table->nr_cap_states - 1;
> > +	unsigned long fmax = cs_table->state[max_cap_state].frequency;
> > +	int i;
> > +
> > +	for (i = 0; i < cs_table->nr_cap_states; i++) {
> > +		u64 cap = (u64)cmax * cs_table->state[i].frequency;
> > +		do_div(cap, fmax);
> > +		cs_table->state[i].capacity = (unsigned long)cap;
> 
> I prefer div64_*() over do_div(), the calling convention the latter
> always confuses the heck out of me.
> 
> So this then becomes something like:
> 
> 		cs_table->state[i].capacity =
> 			div64_u64(cmax * cs_table->state[i].frequency, fmax);

Ok, I'll change both.

Thanks,
Quentin